The proposed project is intended to delineate the pathway of iron through the liver. The number of transferrin binding sites will be determined on isolated mouse hepatocytes with 125I-labeled transferrin binding curves and Scatchard plot analysis. Transferrin-membrane complexes will be solubilized from hepatocytes by detergents then isolated and characterized by gel filtration fractionation and immunoabsorption with anti-transferrin antibodies. Iron binding moieties on the plasma membrane will also be investigated using detergent solubilization of membrane. The kinetics of 59Fe passage through the hepatocyte will be investigated by a series of pulse-chase experiments using 59Fe-transferrin and isolated hepatocytes. The distribution of 59Fe in the various subcellular fractions will be determined and characterized as ferritin, heme, or non-ferritin, non-heme 59Fe.